42
SERVSWITCH
™
BRAND CAT5 KVM EXTENDER
7.3.2 C
ORRECTING THE
PS/2 M
OUSE
I
F
I
T
G
ETS
O
UT OF
S
YNC
On rare occasions, you might notice that, instead of behaving normally, your
mouse pointer is moving and jumping erratically all over the screen (and possibly
selecting things at random). This is usually a sign that the PS/2 mouse has gotten
“out of sync” with the Extender or that the Extender has gotten out of sync with
the CPU’s PS/2 mouse port.
PS/2 mice send mouse data in 3- or 4-byte packets. As long as the CPU knows
which bytes mark the start and end of each packet—which it virtually always does as
long as the mouse is directly connected to it—it can correctly interpret the mouse
signals. But when mice are disconnected and reconnected, or when mouse signals
pass through other devices on their way to the CPU, it is sometimes possible for the
CPU or the intervening devices to lose track of where the mouse-data packets
begin and end, with the result that the cursor/pointer begins behaving bizarrely.
If this happens in some mouse extender/switch systems, the only solution is to
either kill and reload the mouse driver or reboot the PC. But the Extender has a
feature you can use to painlessly recover from this kind of glitch. First try to reset
the mouse as described in
Section 7.3.1
. If this doesn’t work, send the “Null Mouse
Command” in order to resynchronize the CPU’s mouse port. If your Extender is a
Switching model, press and release the hotkey, then press and release the left-
arrow (number 4) key on the keyboard’s numeric keypad (
not
the number 4 on the
top row of the keyboard). If your Extender is a Single- or Dual-Access model, take
these steps:
1. Press and hold down both the left and right mouse buttons.
2. Press and release the Scroll Lock key on the associated keyboard, then release
the mouse buttons.
3. Check mouse operation.
4. If the mouse isn’t yet operating correctly, repeat steps 1 through 3 as many as
two more times. (If this still doesn’t help, call Black Box Technical Support.)
When the Extender receives the Null Mouse Command, it sends a “null byte” of
mouse data to the CPU; this has no effect other than to get the CPU “caught up”
with the mouse. You might have to issue the command as many as three times in
order to get a PC with a 4-byte mouse back on track. Note that, unless your mouse
driver is an auto-correcting type, sending this command while the mouse is in sync
will throw it out of sync.
If the PS/2 mouse frequently gets out of sync in your system, and you’re running
Windows 95/98/2000, Windows Me
®
, Windows NT
®
, or Windows XP
®
, we
